M16 and AR15 rifles are air-cooled, gas-operated, magazine-fed assault rifles. These rifles are the primary assault weapons used by military and police forces.
A gas-operated rifle uses a portion of the high pressure gas formed as the ammunition round travels through the barrel to supply energy to operate the auto-loading feature of the rifle. The high pressure gas powers a mechanism to extract the spent casing and chamber a new cartridge. Energy from the gas is harnessed through either a port in the barrel or a trap in the muzzle. This high-pressure gas travels through a gas tube that is located parallel to the barrel and upon exiting the tube impinges on a surface such as a piston head to provide motion for unlocking the action, extracting the spent casing, ejecting the spent casing, cocking the hammer or striker, chambering a fresh cartridge, and finally locking the action.
Such a modular rifle is illustrated in FIG. 1. As shown in FIG. 2, the rifle comprises a lower receiver assembly 1 conveniently separable from an upper receiver assembly 2. The lower and upper receiver assemblies 1 and 2 are connected using push pins with the pins carried by the lower receiver assembly 1 and extending through openings (not visible in FIG. 2) in the upper receiver assembly 2.
The lower receiver assembly 1 contains a lower receiver, fire control components, and a buffer assembly included in the butt-stock. These components are not separately designated in FIG. 2 and are not pertinent to the structure and function of the present invention. Instead, the present invention relates generally to the upper receiver assembly 2 and its components.
Prior art FIG. 3 illustrates the upper receiver assembly 2, comprising an upper receiver 3 and a hand guard 4 surrounding a barrel 5. The barrel 5 is affixed to the upper receiver 3 using a barrel nut that is obscured from view in FIG. 3 but shown in FIG. 4.
Prior art FIG. 4 illustrates the upper receiver assembly 2 with the hand guard 4 removed to expose a barrel nut 6, a stock gas tube 7 and a gas block 8 that holds the stock gas tube 7 in place. The barrel 5 and the gas block 8 each define a small opening through which gas passes from the barrel, through the gas block, and into the stock gas tube 7.
In the prior art modular rifles of FIGS. 1-4, the barrel 5 is affixed to the upper receiver 3 with the barrel nut 6 and this arrangement requires specialized tools and fixtures to remove and attach the barrel. For example, if the user wishes to change to a barrel of a different length. The prior art design makes it nearly impossible to remove the barrel in the field without use of these tools. Removal also requires a significant amount of time and familiarity with intricate mechanisms of the rifle.